Treatment of wood



Patented Nov. 20, 1945 TREATMENT OF WOOD Clifio'rd I. Haney, Greenwich, Conn., and Mervin E. Martin and Thomas E. McGoury, Cumberland, Md., assignors to Celanes'e Corporation of America, a corporation of Delaware N Drawing. Application February 26, 1943, Serial No. 477,298

11 Claims.

This invention relates to the treatment of wood, and relates more particularly to the production of organic esters of cellulose of relatively high degree of esterification from organic esters of cellulose of relatively low degree of esterification prepared by digesting wood particles with a lower aliphatic acid.

An object of this invention is the provision of an improved process of preparing organic esters of cellulose of relatively high degree of esterification and of satisfactory clarity and color in a rapid, eflicient and economical manner.

Another object of this invention is to provide an improved process for preparing organic esters of cellulose of relatively high degree of esterification by further esterifying organic esters of cellulose of relativelylow degree of esterification produced by digesting wood particles with a lower aliphatic acid and then treating the cellulose pulp under such. conditions that the acylgroups attached thereto during the digesting step are not removed. I

Other objects of this invention will appear from the following detailed description.

Processes for making organic esters of cellulose from wood pulp have heretofore yielded products which were not wholly satisfactory from the standpoint of clarity and color.

We have now discovered that Wood pulp emi nently satisfactory for use in the production of organic esters of cellulose of high clarity and good color may be obtained by digesting wood particles in the presence of a lower aliphatic acid. In'accordance with our invention, wood in aparticle form, for example, sawdust, is first cooked or' digested with acetic acid or other lower aliphatic acid under elevated temperature and pressure. After cooking, the pulp is boiled with acetic acid, and is then subjected to a series of washing operations with progressively weaker acid, and is finally washed neutral with water. The neutral pulp may then be chlorinated, bleached and dried. I a p The partly esterified wood pulp produced by our processis not only of greatly increased purity but; in addition, has a substantial number of acyl groups combined therewith." When this partially es'terified wood pulp is'subjected to further esterification to convert the same into cellulose esters of higher degree of esterification, this partly. esterified cellulose requires the use of less aliphatic acid anhydride to reach the desired higher degree of esterification. Moreover, the present process permits ,of careful temperature control during said esterification reaction and,

accordingly, only a limited amount of cooling is necessary to maintain the temperature of the exothermic esterification reaction within the desired limits. Since the temperature may be maintained under precise control with little refrigeration, the process is very economical and the cellulose ester obtained upon esterifying the cellulose ester of relatively low degree of esterification is of excellent characteristics.

In accordance with our process, the aceticacid or other lower aliphatic acid employed in cooking the wood may be of varying concentrations. Thus, for example, aqueous solutions containing about of the acid, or less, may be employed. However, more concentrated acids, viz. I glacial acetic acid, are preferable. The temperature in the digester may be from to 220 C. and the time of the treatment may vary from 1 to 10 hours. By digesting the wood with acids and then further treating the pulp obtained in ac.- cordance with our invention, the acid may not only be combined with the cellulose to theextent of 5 to 18% by weight (calculated as'the cor.- responding acid) but the additional treatment removes little or none of the combined acid. AS a result, the partially esterified cellulose treated in accordance with our process, -namely, chlorinating, bleaching and drying the same, forms an excellent starting material for further esterification in the production-of cellulose acetate or other organic esters of cellulose.

In chlorinating the partially esteri-fied wood. pulp, chlorine is employed in excess and the excess may vary from 1 to 10% on the weightof the pulp treated. Usually, a chlorination treatment for from 30 to 60 minutes i sufiicient, but opfie mum results are achieved when the chlorination is permitted to proceed for about 30minutes with about 2% of excess chlorine.

The bleaching of the partially esterified WOOd pulp is preferably carried out employing-sodium hypochlorite but sodium chlorite, potassium permanganate or. hydrogen peroxide may also be employed. Whensodium hypochlorite is employed, the solution may containfrom /2 to 3% of avail.- able chlorine and a atisfactory bleach obtained in from 1 to 3 hours with the solution at .Irom 20 to 50 C. We have found that withabout 1% of available chlorine present, optimum results. are obtained in 3 hours at 35 C. a

In order further to illustrate our invention but Without being limited. thereto, the followingflexample is given: I

Example Twenty parts by weight of oven-dry black spruce sawdust are digestedin asuitable digester When the digestion is completed the pulp is boiled twice with glacial acetic acid and is then washed neutral with hot water after being given several washes with progressively weaker acetic acid. After being washed neutral, the wood pulp is subjected to chlorination for 30 minutes with 10% excess chlorine, and following chlorination, the pulp is bleached for 3 hours at 35 C. in sodium hypochlorite with 1% of available chlorine present. The pulp obtained by this treatment has an acetyl value of 15%, calculated as aceticacid.

An acetylation mixture comprising 319 parts by Weight of acetic anhydride, 656 parts by weight of acetic acid and 25 parts by weight of sulfuric acid i cooled to C. and 190 parts by weight of the partially acetylated pulp entered therein. The acetylation reaction takes 1 /2 hours, during which time the peak temperature reached is 45 C. Little cooling of the reaction mixture is necessary to maintain ,the' temperature within the desired limits. At the completion of acetylation, water in an amount sufficient to react with any excess acetic anhydride is added to the reaction mixture together with water for ripening, and the cellulose acetate in solution is ripened or hydrolyzed to the desired acetyl value. 'When the-desired acetyl value is reached, exces water is added to the solution to precipitate the cellulose acetate and the latter is separated from solution, washed and dried.

- The cellulose acetate obtained in the manner described is of excellent characteristics and may be employed in the preparation of textile materials, film, foils, molding powders, coating compositions and the like.

While our invention has been more particularly described in connection with the preparation of cellulose acetate from partly acetylated purified wood pulp cellulose, wood pulp cellulose partly esterified with other lower aliphatic acids may be employed in like manner for the preparation of other organic esters of cellulose. Thus, in accordance with our invention the wood pulp cellulose may be partly esterified and purified, as described, employing other aliphatic acids such as, for example, propionic acid or butyric acid, or mixturesof each of said acid with acetic acid or with each other. In this manner, other cellulose esters such as, for example, cellulose propionate, cellulose butyrate, cellulose acetate-propionate andcellulose acetate-butyrate may be prepared from wood pulp cellulose partly esterified with said acids ormixtures thereof.

While the partially esterified cellulose of relatively low degree of esterification yields cellulose esters of excellent characteristics on further esterification, as heretofore described, we have found that said partially esterified cellulose is also of unusual value as a paper making material. The partially esterified cellulose maybe employed alone or mixed with other fiberssuch as those of chemical or mechanical wood pulp, or rag fibers such as linen and the like, and the resulting material yields an excellent paper stock. Partially acetylated'cellulose of-an acetyl value of 5 to possesses unusually'desirable propertie for use in paper making.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by Letters Patent is:

' ,1. In a process for the preparation of an orgam'c ester of cellulose of relatively high degree of esterification, the steps which comprise digesting comminuted wood with a lower aliphatic acid at a temperature of at least C. whereby the Wood is-pulped and the cellulosic constituents thereof partially esterified, removing the lower aliphatic acid and the material dissolved therein from the cellulosic constituents and, while said cellulosic constituents still retain substantially all of the acyl groups gained during the digesting step, subjecting said partially esterified cellulose to further esterification.

2. In a process for the preparation of organic esters of cellulose of relatively high degree of esteriflcation, the steps which comprising digesting comminuted wood with a concentrated lower aliphatic acid at a temperature of at least 130 C. whereby the wood is pulped and the cellulosic constituents thereof partly esterified, removing the. lower aliphatic acid and the material dissolved therein from thecellulosic constituents and, while said cellulosic constituents still retain substantially all of the acyl groups gained during the digesting step, subjecting said partly esterified cellulose to further esterification.

3. In a process for the preparation of cellulose acetate of relatively high degree of acetylation, the steps which comprise digesting comminuted wood with acetic acid at a temperatureof at least 130 C. whereby the wood is pulped and the cellulosic constituents thereof partly acetylated, removing the acetic acid and the materials dissolved therein from the cellulosic constituents, and, while said cellulosic constituents still retain substantially all of the acetyl groups gained durin the digesting step, subjecting said partly acetylated cellulose to further acetylation.

4. In a process for the preparation of cellulose acetate of relatively high degree of acetylation, the steps which comprise digesting comminuted wood with concentratedacetic acid at a temperature of at least 1309C. whereby the wood is pulped and the cellulosic constituents thereof part- 1y acetylate'd, removing the acetic acid and the materials dissolved therein from the cellulosic constituents and, while said cellulosic constituents still retain substantially all of the acetyl groups gained during thedi'gesting step, subjecting, said partly acetylated cellulose 'to further acetylation.

5. In a process for the preparation of cellulose acetate of relatively high degree of acetylation, the steps which comprise digesting comminuted wood with glacial acetic acid at a temperature of at least 130 C. wherebythe wood is pulped and the cellulosic constituents thereof partially acetylated, removing the acetic acid and the materials dissolved therein from the cellulosic constituents and, while said cellulosic constituents still retain substantially all of the acetylgrpupsgained'dup ing the digesting step, subjecting saidpartially acetylated cellulose to further acetylation,. I

6. Ina process for the preparation of cellulose acetate of relatively high degree of acetylation, the steps which comprise digesting, comminuted wood with glacial acetic acid at a temperature of from 130 to ,220 C. whereby the. wood is p lped and the cellulosic constituent thereof partially acetylated, removing the acetic acidiand the materials dissolved thereinj from thefcellulosic constituents and, While-said cellulosic-constituents still retain substantiallyall of the'acetyl groups ained during the. digesting .step, subjecting said partiallyacetylated cellulose to further acetylation. W,

. -7. In a process for. the -prepar'ation of cellulose wood with glacial acetic acid at a temperature of 1 from 130 to 220 C. for from 1 to 10 hours Whereby the wood is pulped and the cellulosic constituents thereof partially acetylated, removing the acetic acid and the materials dissolved therein from the cellulosic constituents and, while said cellulosic constituents still retain substantially all of the acetyl groups gained during the digesting step, subjecting said partially acetylated cellulose to further acetylation.

8. In a process for the preparation of cellulose acetate or relatively high degree of acetylation, the steps which comprise digesting comminuted wood with glacial acetic acid at a temperature of from 130 to 220 C. for from 1 to 10 hours whereby the wood is pulped and the cellulosic constituents thereof partially acetylated to an acetyl value of from to 18% calculated as acetic acid, removing the acetic acid and the materials dissolved therein from the cellulosic constituents and, while said cellulosic constituents still retain substantially all of the acetyl groups gained during the digesting step, subjecting said partially acetylated cellulose to further aoetylation.

9. In a process for the preparation of an organic ester of cellulose of relatively high degree of esterification, the steps which comprise digesting comminuted wood with a lower aliphatic acid at a temperature of at least 130 0. whereby the wood is pulped and the cellulosic constituents thereof partially esterified, removing the lower aliphatic acid and the material dissolved therein from the cellulosic constituents, chlorinating andbleaching the same and, while said cellulosic constituents still retain substantially all of the acyl groups gained during the digesting step, subjecting said partially esterified cellulose to further esterification.

10. In a process for the preparation of cellulose acetate of relatively high degree of acetylation, the steps which comprise digesting comminuted wood with acetic acid at a temperature of at least C. whereby the wood is pulped and the cellulosic constituents thereof partly acetylated, removing the acetic acid and the materials dissolved therein from the cellulosic constituents, chlorinating and bleaching the same and, while said cellulosic constituents still retain substan tially all of the acetyl groups gained during the digesting step, subjecting said partly acetylated cellulose to further acetylation.

11. In a process for the preparation of cellulose acetate of relatively high degree of acetylation, the steps which comprise digesting comminuted wood with glacial acetic acid at a temperature of from 130 to 220 C. for from 1 to 10 hours whereby the wood is pulped and th cellulosic constituents thereof partially acetylated, removing the acetic acid and the materials dissolved therein from the cellulosic constituents, chlorinating and bleaching the same and, while said cellulosic constituent still retain substantially all of the acetyl groups gained during the digesting step, further acetylating the partially acetylated cellulose.

CLIFFORD I. HANEY. MERVIN E. MARTIN. THOMAS E. McGOURY. 

